[jeffcore]

The President doesn't have the power to unilaterally reimpose criminal consequences, which is what an unpardon would amount to. Instead, subsequent Presidents would have to argue the person was never really pardoned in the first place. George W. Bush did this with Isaac Toussie.

[hackuser]

To be clear, Bush both pardoned and 'unpardoned' Toussie. He wasn't undoing a prior President's action.